C 'RUST 'ACE 'A. 205 



jointed to the spine itself, and the inner posterior margin articulating with a 

 flat thin lamellar spine, which lies in the middle of the membranous 

 expansion. 



Dimensions. The single specimen of this species which has been observed 

 has the following dimensions: Entire length of carapace (the caudal ex- 

 pansion being slightly infolded), 36 mm. ; length of cephalothorax, 21 mm.; 

 length of basal joints of antennae, as far as visible, 9 mm.; width of caudal 

 expansion 17 mm. 



Distribution. In the Erie shales, at LeRov, Lake county, Ohio. 



